Photoelectric detector



SePt- 9, 1952 E. JELLINEK 2,610,232

PHOTOELECTRIC DETECTOR Filed may 5, 195o 2 SHEETS-SHEET 1 SXBT'W WNoulogy dos s uNn o;

AlllA *Sept 9, 1952 E JELUNEK 2,610,232

PHOTOELECTRIC DETECTOR Filed May 5, 1950 2 SHEETS-SHEET 2 25a.- To UNITS FOR FROM ADn/T/o/VAL $51255 ALLEYs 536 I 37 l To ReslsToR 5| To Rcsls'roR 5f oF mRsT ALLeraF secano ALLEY DETECTOR UN\T. DETECTOR UNIT.

I g 35:5 a5 2L w Inventor:

' l' Ernest 'Jelhnek, I i

2z His Attorney.

Patented Sept. 9, 1952 uNiTEo PHo'coELac'rmc DETECTOR Ernest Jellinek, Schenectady, N. Y., assigner to General Electric Company, a corporation of New York Application May 5, 1950, Serial No. 160,177

Thisfinvention relates to photoelectric detection and amplification apparatus, and more par ticularly such apparatus which may be*V convenently'employed as a foul detector for bowling alleys.

yIt` is generally desired tomaintain the distance of all bowlers from thebowling pins at a specified minimum in order to assure equal opportunity for accuracy for every player. For this purposefa so-called foul line is generally marked at the end of the alley from which the bowling ball is delivered. No player is supposed to cross this foul line as the ball is delivered. Since 4dispu't'esmay arise between Vplayers as to whether Ithe foul line' has been crossed or not, it is ldesirable to have some automatic-means for detectionof'affoul. The photoelectric cell-has been found quite satisfactory for this purpose. However, in order to obtain an indication from the photoelectric cell to show that the foul line has been crossed, itis necessary to have means for amplifying the signal of the photocell to operate some signaling means.

yIt is therefore an object of this invention to provide an improved photoelectric foul detector apparatus including animproved and simplifiedmeans for amplifying the photoelectric'signal and operatingv asignal device.

The American 'Bowling Congress has specified thatl such a fouldetectorapparatus shall ring a signal bell for from one to two seconds and illuminate-1a signal light at the alley where the foulfis committed for from ten to fifteen seconds. One signal bell may be used for a large number ofalleys, but a signal Vlight vmust be used -for each alley. f

It :is ltherefore an object of this invention to yprovide afoul detector apparatus which will satisfy theV abovespecifications but which is at the Sametime simple, economical, reliable and requiring a minimum of adjustment at the time of installation and during use.

DuringV use the voltage supplied to the ap-` eration of prior apparatus of this description..

Itis therefore a further object of this invention to provide an apparatus of the above description which will operate reliably over relatively wide ranges of fluctuation of line voltages.y

andv steady state illumination;

Itis inevitable that where alight beam which` is focused upon a photocell is placed so as to be interrupted by a bowlers foot which crosses 5 Claims. (Cl. 175-321) the foul line, it may also be interrupted by the .passage of the bowling ball as the ball is delivered. Delivery of the ball may therefore interrupt the beam on many occasions where no .foul'occurs It is therefore a further object of the invention to provide an apparatus of the above description Iwhich will not be operated by the'brief interception of the light beam due to passage ofthe bowling ball, but which will be operated by passage of a portion of the bowlers body across the foul line. In carrying out the objects of this invention an apparatus which may be employed includes a suitable power supply unit, a signal bell unit, and an individual alley detector unit for each of the bowling alleys to be equipped. A portion of the power which is supplied to each of the alley detector units passes through the signal bell-unit in such a way that, when an alley detector unit is actuated by the occurrence of a foul, a greater power supply flow to the actuated alley detec'tor unit causes a change in voltage in a portion of the signal bell unit to actuate a signal bell. v

For a more complete understanding of the in- .vention reference should be had to the following specification and the accompanying drawings, in which Fig. 1 is a schematic diagram of one embodiment of the apparatus of the invention, Fig. 2 is a schematic diagram of a portion of -the apparatus showing an alternative embodiment, :and Fig. 3 is a schematic diagram showing another alternative embodiment.

Referring more particularly to Fig. l, there is shown a power supply unit l, a signal bell unit 2. and one or more alley detector units 3 for the respective bowling alleys 4. Any reasonable .number of alley detector units may be employed in this apparatus in conjunction With one signal bell unit. In practice, this number has generally been limited to sixteen, but a larger number could be used. Since all of the units 3 are substantially identical, in the interest of simplicity and -cla-rity in this specification the detector unit for only the first alley is-shown and described indetail.

Electrical power may be supplied from a suitable source to the incoming terminals 5 of the power supply unit l and thus to a power transformer E within the unit. The secondarywind- :ing l of transformer G may be connected to a Ifull wave rectier 8, the output of which maybe connected through a suitable lter such as that including capacitor `Si and resistors l0 and l l, and

a voltage regulating glow tube I2 to provide a p-late supply voltage of a suitable magnitude such as 150 volts at connection i3. This voltage is .positive with respect to the ground connection at I4 from the -center tap of transformer winding 1.`

Negative grid bias voltages and the plate supy ply voltage for the phototubes may be obtained by a second rectifier l5, poweredfrcmfa'tap on transformer rwinding 1,7the output of which may be suitably ltered by a capacitor I6 and resistors I1 and I8. available from this source is taken at I9 for a A portion of the voltage.:i215` lnegative 50-volt 'sourcesupplied by? connection 31. This negative bias voltage is also supplied to the grid 4Gb of device 49 through a grid resistor grid bias supply voltage of approximately minus 'Y 50 volts from the mid-connectionof resistors I;1; g

and I8. The full voltage from rectifier I may be further filtered by the combination of resistor 29 and capacitor 2I for a phototube plate supply .of approximately minus 70 volts :Walla-ble at creates a voltage drop in cathode follower resistor :connection 22. Y

The signal bell unit 2 includes a signal bell 23, a bell actuating relay 24, agrid controlledeelectron discharge device for energizing relay 24 and a capacitor 26 for timing the signal bellV operation. A resistor 21 is provided in series with capacitor 26 for limiting the capacitor current. The relay 24 is provided with main signal bell circuit contacts 28 and auxiliary contacts 29 and 30 for changing the connections to capacitor 26 upon actuation of the signal bell2 circuit. vThe control grid 2573` of discharge device 25-is supplied Vwith a suitable Vbiasvoltage through resistors 3| and 32 by means of a potentiometer 33 whichA is connected between ground and the minus 50.volt grid bias voltagesupply.V The grid is controlled by a circuit including a capacitor 34 and a resistor 35 in a manner which will be described below.

Power is available to the alley `detector units 3 from the signal 4bell unit 2 byjmeans of connections whichare respectively designated at 13.36,' 31 vand 22. Each of the alley detector units 3 is associated with aseparate bowling alley 4, and connected to a suitable signaling device such as light 38. In each unit 3 there is provided a re` lay 39 for energizing signal light 38, a grid controlled electron discharge device 40 for energize A ingvthe relay 39, a timing capacitor4 IV for timing a period of energization of relay 39,a secondgrid controlled -electron discharge device 42 for controlling the energization of device, 40, and a phototube 43 for controlling the energizatioriofV device V42. The phototube 43 is normally illumie nated from a source such as a lamp 44. The

e illumination may be directed tothe phototube by means such as a condensing lens 45'. 'Ifhis-di-v rected beam of light preferably crcssestlie bowling alley in the vicinity ofthe foul line. Itis une derstood that the light beam maycrcssand recross the foul line a number` of times 4by use of reective mirrors or* prisms (not shown), in order toalord the opportunity for interception of the light beam over a larger area than could be covey eredby a single crossing. i

e The illumination normally falling on phototube 43 from light source 44causes `thetube to be `conductive by reason ofthe plate voltageappearing across the tube between connections 36 andf22; the phototube current being limited by a-l series resistor 46. The phototube current causes a voltage drop across resistor 46 which holdsthe control grid of discharge device 42v at a substantial negative voltage, thereby preventingconduction by discharge device 42. e i

Relay 39 is equipped with main vcontacts' 41 Vfor closing a circuit to signal light 38 andauxiliary If a `foul' is committed, interrupting the beam .eoflight from source 44 to phototube 43, the ,.phototubecurrent decreases and the voltage drop across resistorY 46 decreases which raises the potential of the control grid 42-b of the device 42 to cause a plate current in device 42. This current 5I which raises the potential of the control grid 49o of devicehllcausing a plate current in device ee. The e011 of relay se is .une energized Vby de vice 49 closing contacts'41 and illuminating the signal light 38. ARelay contacts48 are. likewise closed and contacts 49 opened. Thel snorting connection across capacitor 4I is thereby broken by the contactsdil, and the uncharged capacitor 4I is connected through contacts48 andv relay coil 39 to the positive supply connection I3.. The grid 49h of device 40 is thereby connected to the positive supply connection I3 through the capacitor 4I, and device 40 will therefore remain conductive,Vv holding relay 39 picked ,up; and signal light 3S on, until capacitor 4I charges through the charging path including the winding Yofrelay 39, contacts 48, the capacitor itselfresistcr 59, and cathode -biasfresistor 5Ito thenegative bias connectionl and the parallelcharging path including resistor 52andigrid 40h to cathode 40a to connection 36,. The resistances of cathode bias resistor 5I and grid resistor 52 are largein comparison to` the combined resistance of resistorlb and the Winding of relay 39, so that the initial connectioncof capacitor 4I in the circuit establslies` a definite `positive voltage cn grid 4Gb. Phototube 43 is isolated-fromdirect connection to capacitor 4I by discharge device 42.v A v As capacitor 4I gradually charges, the potential of grid 40h will gradually 4decrease and then go negativelv because-of the negative grid bias voltage derivedl from connection 31 through cathode follower? resistance 5 I. tothereby cut off device 49. When; device 4 0 ceases to be conductive the re-v lay 39;1`s again dev-energized andthe signal-light 38 is thusswitchede 01T 'by the opening- 4of relay contacts 4T. Thus the signal light 38 is illuminatedior a predetermined periodici time after the foul is .committed and'A this period is: prefer-'- ably that specified bythe American *Bowling Congress, asmentioned above,l at 'from ten to. fteeniseccnds. This on.peri"od isdetermined by proper selection of capacitor'flll and'lthe ire-'e sistors 50, 5I and 52'which comprise main charging paths for capacitor 4I andthereby determine the charging time. Upon. de-energizatiom. relay contacts 49 close and discharge capacitor`4 4IV through rresistor 53, and reconnect grid ,40brto i the lfouledetectorgsince -no foul has vbeencom` mitted. -A foul is therefore distinguished Vfrom .aardgas passage of the ball in terms of the relative perlods'of interruption of the light beam, the interruption'by the ball being relatively brief, and the interruption by the player himself in committing the foul being relatively longer. A suitable time delay in theioperation of the circuit isprovided to distinguish between these two conditions by means of capacitor 53 which is connected between grid 46h and anode 40e of the discharge device 40. This time delay is operative upon initial conduction in the plate circuit of discharge device 40. Such initial conduction causes a voltage drop across the relay winding of coil 39, and this voltage drop is in effect subtracted from the 150 volt plate supply which is connected at I3 through the relay winding to anode 40e of device 40. Since anode 40e and grid 40h are interconnected by capacitor 53, such a lowering of the plate voltage is initially transmitted to grid 40h in almost its full magnitude to therebyv depress the voltage on grid 40h and limit the conduction in discharge device 4I! until capacitor 53 charges. A grid filter capacitor 54 may also be provided.

The time delay obtainable by means of capacitor .53 may be alternatively obtained without capacitor 53 by enlarging grid capacitor 54 so that an appreciable time is required to change the voltageV of control grid 40D upon application of a new voltage to the resistor 52. of this alternative time delay may also be improved by reducing the amount of negative grid voltage available at connection 31 from the minus fifty volts to the order oi.v minus twelve volts. Since this alternative time delay method involves only .a minor change in the circuit, `that is, the elimination of capacitor`53, no separate diagram for this alternative is shown.

As discharge device 40 becomes conductive, the

current supplied to the cathode 40a throughy connection 36 causes a voltage drop across resistor 35 in the signal bell unit 2. This voltage is connected through the capacitor 34 'to cause a rise in the potential of control grid h of electron discharge device 25, causing device 25 to become conductive. The plate curent of device 25 then energizes relay 24, closing relay contacts 28 to energize signal bell 23. At the same time, relay contacts 29 open to disconnect a discharging circuit for capacitor 26, and relay contacts 30 close to connect capacitor 26 through resistor 21 to the grid 25h of discharge device 25. Since capacitor 26 is initially discharged, this connection applies a positive voltage through capacitor 26 from the plate voltage supply connection I3 to the grid 25h, causing this grid to remain positive and device 25 to remain conductive until capacitor 26 charges through the path afforded by resistance 21, relay7 contacts 30, resistance 32, and potentiometer 33. An appropriate periodof operation of relay 24 is thereby obtainable for a charging period of capacitor 26 independently of the duration of the signal derived from operation of device 40. This period is determined by the capacity of capacitor 26 and the resistance values of charging path resistances 21, 3I, 32 and 33, and is preferably the one to two seconds specified-by the American Bowling Congress.

In the modification shown in Fig. 2, the resistor has been moved in signal bellunit 2 from kthe circuit between ground connection I4 and connection 36 to the circuit between input connection I8 and output connection 31. A signal, isv noA longer derived therefore by the Agrid Operation l6 25h ofthe `device 25 by reason ofthe. cathode currents of vcathode 40a of device 40 in the alley detector unit 3. Instead, resistance 35 is now in acharging circuit of timing capacitor 4I of the detector unit 3. Thus a portion of the positive voltage which is applied to grid 40h of device 40 during the timed period of signal' light actuation obtained by the timing capacitor 4I is also applied to grid 25h of device 25. The relative values of resistor 35 in the signal bell unit 2 andresistor 5I in the detector unit 3 may be so chosen that the desired time delay causing signal bell operation of from one to two seconds may be obtained from the detector unit timing capacitor 4I. Thus the capacitor 4I times the duration of operation of both signal light 38 and signal bell 23 and the relatively expensive capacitor 26 may be eliminated. Also, it will be seen that in Fig. 2 resistor 21, relay contacts 29 and 30, resistor 32, potentiometer 33, and capacitor 34 have been eliminated, thus further simplifying the signal bell unit 2.

. In order to have the Fig. 2 modiiication operate correctly for a number of alley detector units, without causing unwanted operation of discharge devices 40 in detector units where a foul has not occurred, due to the voltage at connection 31 which is intended only to operate signal bell unit discharge device 25, the cathode 25a. of discharge device 25 is preferably connected to a source of voltage which is negative with respect to the cathodes of -discharge` devices 40 and therefore negative with respect to the connection 36. This may be obtained, for instance, by connecting the cathode 25a of device 25 to the midconnection of two series-connected resistors 60 and 6I which form a voltage divider between input connections I4 and I9 which are respectively at ground potential and at minus 50 volts. By this means the device 25 may be operated by a voltageat resistor 35 vappearing at connection 31 which is too low to operate devices 40 in the unactuated detector units.

In Fig. 3 there is shown a further modification of the signal bell unit wherein the voltage divider resistors 6I] and 6I are not employed, but the cathode 25a of device 25 is connected directly to ground connection I4. In order to avoid false operation of otherwise unactuated alley detector units, a separate discharge device 25 is employed in the signal bell unit for each alley detector unit. This modication is useful for small installations, as for only one or two bowling alleys, where the cost of additional devices 25 does not exceed the cost of the signal bell unit timing capacitor 26 employed in the embodiment of Fig. l.

The operation of the signal bell units in all of the embodiments shown, whereby a signal appears at a resistor 35 in response to operation of one of the alley detector units, may be described in the following terms. The power supply unit I provides power through the signal bell unit to the alley detector units 3. When any one of the alley detector units becomes operative, the greater current flow between the power supply unit and the operative alley detector unit creates a signal in the resistor 35, which is employed in the signal bell unit to operate the signal bell. It will be' seen that operation of any alley detector unit will create a signal at resistor 35 to actuate the signal bell unit 2.

Although for convenience and clarity in presentation, the apparatus of this invention has been described in terms of a power supply unit, a signal bell unit, .and various alley detector units,

sae-10,232

envelopes a more satisfactoryselection'of device .types-is obtainable, however, if the device `l2 iis combi-ned withthe-:device 2 in aniadjacentr alley fd'etector'unit andzdevicel 4is likewise combined `vwit-hfdevice lfie/in an adjacent ldetector unit; :Deev

tector units are therefore more i Iconveniently added in pairs. I Y.

Referring, again to Eig. l.; the -iilainentheater elements '55, 56 Vand :5l fof `discharge devices 25, `Zand ,4U are supplied, as indicated bythe letters by the `filament transformerfsecondary wind-V ing 158 on power transformer 6.' .This filament supplyv/inding158,'ins'teadlof being grounded, is connected by a conductor '59 'to the -mid tap oi resistors lj'l'a'nd I8. ABy reason ofthisrconnection no, interference is occasioned with thevcathode vfolloweroperation'of discharge device `42, Whereas with the lainent connected directly to ground', the resistance betweenthe filament heaters B and the assooiatedcathodes 42a providesa re.

sistance path for thecathocle to ground, whichV interferes with the cathode /follower response desired.- g .Y ,v

YIt isto be seen that the timing circuits of this apparatus, -includingthe timing capacitors 26, dll-and 53 provide time'delay periods. whichare relatively independent vof both the vgeneral level i of illuminationl and thevoltage supplied 'tothe phototube as long as phototube operation is satisfactory to initially vactuate the detector unit. Being-relatively uncritical in adjustmentjand operation, the apparatus may be easily installed to give-along life of trouble-free operation, while at the same time being simple in structure and therefore economical to manufacture. vIt, is therefore apparent that this invention provides an improved, reliable, durable and economical photoelectric detection apparatus which is very suitable for use as a bowling alley `foul detector.

While certain specio embodiments have been shown and described, it will be understood that various modifications may be-'rnade without departing from the invention. The appended claims are ltl'ierefore intended to cover any 'such modiiications within the A`true :spiritfand scope of the invention.

g What Si claim as new aand desire -to--secure by Letters Patent ofthe United States, :is: n,

fl. A Arelay 'controlrsystern comprising -a `pair-oi? voltage'supply conductors, a first electric valve having an anode, -a cathode and a 'control'elec- VVtrode, ia connection from saidanode tooneof said supply conductors. -a connection from; said cathodeto the lotherY of: said suppl-y conductors, means for producing 'a beamof light, a 'control circuit vincluding an impedance 4anda photoelec-l tric cell responsive to 'an interruption oi" .said beam for producing a change in theV voltage across 'said impedance, an electric valve amplifier connected to be responsive ito 'the Voltage 'across Y said impedance 4and 'connectedfftorsaid .control electrode. and. cathodefor supplyingfiaf corre.

spending' :changed voltage 'thereto to initiate-.a current .ain the `anemie-cathode'circuit of l Ysaid valve, anY electromagnetic 'switching device ihav.- ing main load controlling contacts' and fan'zoperating vcoil connectedgin said `rst lconnection l'and responsive to axp'red'etermined' value ofic'urrent in said:anodecatlfiodecircuit'ior picking up Asaid switching*devicejandtnieans `iordelayingthe'p'ick up ofrsaid switching `device ``for apredetermin'ed interval-of timeafter the interruption ofk .said 'light-:beam comprising a resistorconnected in circuitwith said controlelectrodeand a capacitor lconnected:between said yanode and .said control Velectrode for controlling the rate "of increase of current 'in'said anodeeca'thode circuit.

2. Al-relay controlfsystem comprising -a'p'air oi voltage supply conductors, fa first .electric valve .having an 'anode, 'a 'cathode'and a control electrode, connection tfroin .said 'anode to' a rst of vsaidxsuplzily conductors,a connection from said cathode to the other fof said 4supply conductors, asourceeo Ylight,a.control circuit including-'an impedance vand a plfiotoelectric*.-c'ell responsive to a change in the amount of said 'iight ifor pro- -ducing a corresponding Vchangein the voltage across :said impedance, ffan 'electric valve ampli- -ier responsive Vto"s'aidich'ang'ein voltage for supplyingfafcorrespondin'g change Iinvoitage between' said control electrode; 'and cathode; to vary the current in the' ancde-cathodecircnit `of 'said first electric valve, an e'iectromagnetic :switching vdevice having main` load controllingeontacts and Yhaving an `operating-coil connected in said anode connection and responsive vto "1a predetermined value of "currentin said'anodeecathodecircuit vfor picking up said 'switching 'devicatmeans ufor jproie vidinga 4predetermined*time interval between the occurrence of said change :in light vand `the pick -upiof said switching device vcomprising a resistor 4included in'circuit "with said controlV elec- .trode and Aa capacitor connected between said anode .and Asaid control electrode, a time delay circuit comprisinga resistor andacapacitor connected in' series to said controlelectrode and to said second supply conductor, auxiliary normally closed contactsfen'said-switching vdevice normally completing a short-circuit-around said'last mentionedl resistor andcapacitor and opened in the picked up position fof vsaid switching -device to interrupt said short-circuit .and to 'interrupt fthe supply'of Voltage froinsaidaniplier -to 'saidconf trol electrode, and normally `vopen.contacts on said switching device closed in Ythe picked up position of -said switching device to complete the connectionof saidcontrol electrode through said last mentionedvcapacitor and resistor to :said'rst supply conductor to maintainrsaidswitching de- `Vice tpicked `up for -a predetermined-interval of time. Y

control Ysystemcornprising in combinatio'n, a pair of voltage supplyY conductors, an electricV valve having Aan anode a cathode anda control electrode and havingits 'anode connected to the first of saidconductors 'and its cathode connected to the second ofV isa-id conductors. aA first resistor includedin the connection between said-,cathode and'said second conductor, means for biasing said valve inthe regionof cut off comprising a circuit including a photoelectric cell and a second 'resistor connected fin-series relationship I'and connections from: said second re'' sistor to -the control electrode cathode circuit Vof said valve, a second .electric valvelhaving `afcontrol electrode, an aancde "connected 'to said first conductor, ja cathode connected to anintermedi--A ate voltage point between said first and second conductors, connections from said rst resistor to the cathode and control electrode of said second valve, an electromagnetic switching device having an operating coil in the connection between the anode of said second valve and said first supply conductor and having normally closed contacts in said connections, and means providing a time delay between the response of said photoelectric cell to a light change and the pick up operation of said switching device comprise a resistor connected between the cathode of said first valve and the control electrode of said second valve and a capacitor connected between the anode of said second valve and the control electrode of said second valve.

f4. A relay control system comprising in combination, a source of light, a control circuit including an impedance and a photoelectric cell connected in circuit therewith and responsive to a change in the amount of light received from said source for producing a corresponding change in the voltage across said impedance, an electric valve amplier having output terminals and having an input circuit connected to said impedance device and responsive to changes in voltage across said impedance device for producing corresponding changes in the voltage across said output terminals, a pair of supply conductors, an electric valve having an anode, a cathode and a control electrode and having its anode-cathode circuit connected across said supply conductors, connections from said output terminals to said control electrode and cathode to effect variations in the current in said anode-cathode circuit in response to said light changes, an electromagnetic switching device having contacts for controlling the connections from said output circuit to said control electrode and cathode and having an operating coil connected between said anode and one of said supply conductors and responsive to a predetermined value of current in said anode-cathode circuit for actuating said contacts to interrupt the supply of control voltage to said cathode and control electrode and means for delaying the operation of said relay for a predetermined interval of time after said variation in light comprising a resistor connected between one of said output terminals and said control electrode and a capacitor connected between said anode and said control electrode.

5. A relay control system comprising a pair of voltage supply conductors, a first electric valve having an anode, a cathode and a control electrode, a connection fromL said anode to a rst of said supply conductors, a connection from said cathode to the other of said supply conductors, a source of light, a control circuit including an irnpedance and a photoelectric cell responsive to a change in the amount of said light for producing a corresponding change in the voltage across said impedance, an electric valve amplifier responsive to said change in voltage for supplying a corresponding change in voltage between said control electrode and cathode to vary the current in the anode-cathode circuit of said rst electric valve, an electromagnetic switching device having main load controlling contacts and an operating coil connected in said anode connection and responsive to a predetermined value of current in said anode-cathode circuit for picking up said switching device, means for providing a predetermined time interval between the occurence of said change in light and the pick up of said switching device comprising a resistor included in circuit `with said control electrode and a capacitor connected between said anode and said control electrode, and auxiliary normally closed contacts on said switching device opened in the picked up position of said switching device for interrupting the supply of voltage from said amplifier to said control electrode.

ERNEST JELLINEK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,044,164 Gulickson June 16, 1936 2,060,500 Hitchcock Nov. 10, 1936 2,112,228 Crago Mar. 29, 1938 2,425,257 MacLagan et al. Aug. 5, 1947 2,455,909 Smith Dec. 7, 1948 

